1. Field of the Invention
The present invention relates to an image recognition apparatus to be used in automatically executing die bonding, wire bonding or the like in semiconductor manufacturing steps so that a position of an electrode of an element can be detected automatically and precisely.
2. Description of the Prior Art
In general, an electrode of a transistor, a diode or the like formed in a semiconductor device, for example, an integrated circuit is rectangular and has sides which are about 100 .mu.m in size. For this reason, in the case where a wire is to be provided on the electrode, image recognition is utilized in order to precisely detect a central portion of the electrode. An image recognition apparatus to be used has a structure in which light is radiated on the electrode as an object from a light source such as a tungsten lamp or a halogen lamp, the light reflected by the electrode is photoelectrically transferred by means of image pick-up means such as a CCD camera or an ITV camera so as to obtain an image signal, the image signal is converted into a binary signal, the binary signal is graphically processed to be compared with an area preset value or a reference pattern, and a central position of a recognition pattern of the electrode as an object to be measured is detected or the quality of the electrode itself is decided (see Japanese Unexamined Patent Publication No. 1-227443).
The material of the electrodes depends on elements formed in an integrated circuit. For example, an electrode such as a transistor is made of aluminum, while an electrode of a light emitting diode or hall element is made of gold. In addition, an oxide film is formed on the surface of the electrode. For this reason, it is required to variably adjust the luminance or luminescent color of the light source so as to be suitable for the material of the electrode or the like in such a manner that a stable image signal can be obtained.
Referring to the lamp which is used as the light source, however, the luminance is not quickly responsive to the change of supply power. Consequently, it takes much time to stabilize the lamp. Since the luminance of the lamp cannot be feed-back controlled at a high speed, it is open-loop controlled by varying a current value supplied to the lamp according to a volume. Consequently, it is impossible to precisely adjust the luminance.
The luminescent color of the lamp can be varied by only a filter. A variety of filters cannot be arranged in a package. It is proposed to use a special light source which is provided with filters corresponding to the electrodes having different materials formed in the integrated circuit. However, the entire apparatus is large-scaled so as not to be put to practical use. Consequently, the luminescent color is not varied correspondingly to the electrode.
Furthermore, the lamp is comparatively large-sized and generates much heat. Consequently, only two or three lamps can be arranged in the package. Therefore, a uniform face emitter cannot be formed, so that a precise image signal cannot be obtained owing to the shadow of the object.
As described above, the brightness of the light source cannot precisely be adjusted, the luminescent color of the light source cannot be varied, and the uniform face emission cannot be carried out. Consequently, the recognition pattern of the electrode is not correct. As a result, the central portion of the extremely small electrode cannot precisely be detected and the quality of the electrode cannot precisely be decided, so that a yield is lowered.